Bulma, the flexbox-based css framework makes website design painless. If you don't know what flexbox is, you have missed one of the most important css features of the last years.
To put it in the nutshell, flexbox allows working with rows and columns to distribute the available space. This concept has been used in gui layout managers for many years but was missing in css. Many frameworks aimed to either mimic or substitute this feature with their own "grid layouts". Since the introduction of flexbox in 2017 making flexible, responsive layouts has become a lot easier. However, many other frameworks still support the old "make do" approach along with flexbox which adds some overhead.
Bulma comes with just enough classes and components to quickly build a responsive web site.
As with most modern css frameworks Bulma uses sass which means that you can easily build a customized version. However, if you don't want to you do not have to. You can either include a link pointing to the cds version or host the pre-built version without any modifications.
If you are familiar with sass, not only can you customize bulma, tweaking things such as colors, typography, breakpoints and many other things, you can also include only those parts that you actually need.
For more information: https://bulma.io/